Gas turbine engines, such as those used to provide thrust to an aircraft, are internal combustion engines that use air as the working fluid. In general, gas turbine engines may include a fan section and a core engine located downstream of the fan section. In and upstream to downstream direction, the core engine may generally include a compressor section, one or more combustors, and a turbine section. During operation, air may be drawn into the fan section and may be accelerated by the rotating blades of the fan. A fraction of the indrawn air may then be routed through the core engine, where it may be compressed and pressurized by rotating blades of the compressor section before entering the combustor(s). In the combustor, the air may be combusted with fuel to generate hot combustion gases. The hot combustion gases may then expand through and drive the turbine section which may extract energy from the gases to power the compressor section and the turbine section. The gases may then be expelled through an exhaust nozzle to provide forward thrust to an associated aircraft, or to provide power if used in land-based operations.
Prior to entry into the combustor(s), the compressed air exiting the compressor section may have a high temperature and may be traveling at a high velocity. In order to guide the air to the combustor, as well as to reduce the velocity of the compressed air and to condition it for combustion, the gas turbine engine may also include a diffuser case. In particular, the diffuser case may be made up of two components, an inner diffuser case and an outer diffuser case. In addition, the engine may have a pre-diffuser at an outlet of the compressor section which may define a radially-diverging passage for the compressed air exiting the compressor section. Specifically, the passage formed by the pre-diffuser may expand in area from an inlet to an outlet of the pre-diffuser, thereby allowing a reduction of the compressed air velocity via area expansion before it enters the combustor(s). Typically, the pre-diffuser is a feature of the inner diffuser case.
Pre-diffusers may also include a plurality of structurally-supporting struts extending radially between an annular inner wall and an annular outer wall of the pre-diffuser. For example, U.S. Pat. No. 4,198,926 discloses a gas turbine engine pre-diffuser with wedge-shaped struts between the inner and outer walls of the pre-diffuser. While effective, pre-diffuser struts may serve little to no aerodynamic purpose other than enhancing the structural rigidity of the pre-diffuser.
Clearly, there is a need for improved strut designs for pre-diffusers in gas turbine engines.